1. Field of the Invention
This invention relates to a semiconductor single crystalline substrate for vapor-phase growth of an epitaxial layer on the main surface thereof and a method for the production thereof. More particularly, this invention relates to a semiconductor single crystalline substrate such that, when the vapor-phase growth of a very thick epitaxial layer is in process thereon, the otherwise possible occurrence of edge-crowns is precluded by the usage of the substrate and a method for the production of the semiconductor single crystalline substrate.
2. Description of the Prior Art
The technique of vapor-phase epitaxial growth resides in attaining vapor-phase growth of a single crystalline thin-film layer for use in the production of such integrated circuits as bipolar transistors and MOSLSI's. This technique constitutes a very important method because it allows epitaxial growth on a clean semiconductor single crystalline substrate with a uniform single crystalline thin film of which crystal orientation is identical with it of the semiconductor single crystalline substrate and permits formation of a steep impurity concentration gradient having a junction with a large difference of dopant concentration.
The reactors for vapor-phase epitaxial growth are known in three types, i.e., the vertical type (pancake type), the barrel type (cylindrical type), and the horizontal type. These reactors share a common operating principle of accomplishing the growth of an epitaxial layer, by first, mounting a given semiconductor single crystalline substrate on a susceptor which is a heating plate made of a graphite having a dense SiC coating provided on the surface of the plate, heating the substrate to a predetermined reaction temperature, and introducing a raw material gas into the reaction site for growing an epitaxial layer by thermal decomposition or reduction with hydrogen.
The semiconductor single crystalline substrate, for the sake of allowing an epitaxial layer of high quality to be grown thereon, is furnished with various devices.
The periphery of the semiconductor single crystalline substrate is given a beveled edge by a work called a chamfering. The substrate, while being handled or conveyed, tends to sustain cracks or chippings on the periphery thereof by collision against a hard object. The semiconductor single crystalline substrate, while the vapor-phase epitaxial growth is in process, induces abnormal growth called an edge-crown on the periphery thereof. The chamfering, therefore, is required to diminish these detrimental phenomena. Numerous inventions covering this technique of chamfering have been applied for patent. JP-A-49-43,881 as issued from one such patent application.
When a silicon epitaxial wafer with a very thick epitaxial layer is to be prepared for use such as, for example, in the production of such high breakdown voltage large-current elements as IGBT (insulated gate bipolar transistor) which are creating growing demands in recent years, the silicon epitaxial wafer to be used therein forms edge-crowns (62a, 62b, and 62c) of a hardly ignorable height in the peripheral part thereof on the obverse and on the reverse side as illustrated in FIG. 8, though this silicon epitaxial wafer has undergone the chamfering work. The dimensional tolerance heretofore observed in the chamfering work performed on the peripheral part of a substrate has been specified on the assumption that an epitaxial layer is to be grown to a thickness of some tens of micrometers at most. It is not necessarily proper for application to the growth of an epitaxial layer having a thickness exceeding 100 .mu.m.
When a very thick epitaxial layer is grown by the use of a vertical type reactor for vapor-phase epitaxial growth, the edge-crowns mentioned above occur in the peripheral part of an epitaxial wafer on the main obverse side and on the reverse side. The positions where the edge-crowns occur in the peripheral part of the substrate are fixed by the plane orientation of the substrate. When the plane orientation of the main obverse surface is {100}, for example, the edge-crowns occur each at four positions near the peripheral part of the main obverse surface in the direction of &lt;011&gt;.
As illustrated in FIG. 8, the edge crown 62a which occurs on the main obverse surface side (hereinafter referred to as "front crown") is formed on the interface between an epitaxial layer 63 grown on the main obverse surface side of a single crystalline substrate 51 and a facet appeared on a chamfered part 52. The edge crowns 62b and 62c which occur on the reverse surface side of the single crystalline substrate 51 (hereinafter referred to as "rear crowns") is formed on the interface between an epitaxial layer grown around the chamfered part on the reverse surface side of the substrate 51 and the facet appeared on the chamfered part 52 (62b), and on a plane in such a manner as to cover the edge of the peripheral part of a protecting film 53 for preventing the phenomenon of autodoping (62c).
The height of the edge-crowns are measured by referring the main obverse surface and the reverse surface of the single crystalline substrate 51 as the standard planes. The height Hi of the front crown 62a is measured by referring the surface of the epitaxial layer grown on the main obverse surface of the substrate 51 as the standard plane, and the height H2 of the rear crowns 62b and 62c is measured by referring the reverse surface of the substrate after the removal of the protecting film 53 as the standard plane.
When a conventional semiconductor single crystalline substrate is used, the height H1 of the front crown 62a, can be reached to 30 .mu.m in an epitaxial layer grown to about 100 .mu.m, depending on the growth conditions. If the height H1 of the front crown 62a exceeds 10 .mu.m, the subsequent process of a device fabrication will be at a disadvantage by causing the front crown 62a to contact with a mask for the formation of a photolithographic pattern at the peripheral part and consequently impairing the contact tightness between the mask and the epitaxial layer 63 and degrading the sharpness of the pattern.
If the height H2 of the rear crowns 62b and 62c exceeds 10 .mu.m, since the single crystalline substrate 51, while being vacuum chucked on the reverse surface side thereof, is bent concavely with the peripheral part thereof pushed up by the rear crown 62b, the subsequent process of a device fabrication will be at a disadvantage in impairing the contact tightness between the mask for the formation of a photolithographic pattern and the epitaxial layer 63 and consequently degrading the sharpness of pattern in the same manner as the front crown 62a occured on the main obverse surface side. Also, if the height H2 of the rear crown 62b exceeds 10 .mu.m, the single crystalline substrate 51 tends to be coupled with the susceptor during the growth of the epitaxial layer 63 and, deformation due to the thermal stress generated between the coupled spots of the substrate and the susceptor during cool down will eventually cause cracks and slips.
Heretofore, in the growth of a very thick epitaxial layer, efforts have been made to confine the heights of edge-crowns within 10 .mu.m by suitably selecting the type of a vapor-phase growth reactor, the shape of a pocket of the susceptor for retaining the substrate, and the growth conditions such as reaction temperature and growth rate.
When a barrel type vapor-phase growth reactor is used for growing an epitaxial layer in the place of the vertical type vapor-phase growth reactor, edge-crowns occur exclusively on the main obverse surface side. Since this type of reactor retains a single crystalline substrate by tilting against a substantially upright susceptor, and consequently an area of the chamfered part of the single crystalline substrate contacts with the lower lateral wall of the pocket of the susceptor inevitably, the contact area of the chamfered part of the single crystalline substrate tends to be coupled with the lower lateral wall of the pocket via the epitaxial deposition and inflicts cracks and slips thereon when the epitaxial layer is grown very thick.
When the depth of the pocket of the susceptor for retaining the substrate is made deeper, the reaction gas supply to the periphery of the poket becomes less. Thus, the height of edge-crowns decreases as the depth of the pocket is deeper. On the other hands, the epitaxial layer thickness becomes thinner by a low growth rate at the periphery of the layer, resulting the thickness distribution becomes worth.
The height of the front crown becomes lower and that of the rear crowns becomes higher when the growth rate is increased. Conversely, the height of the front crown becomes higher and that of the rear crowns becomes lower in proportion as the growth rate is decreased. In short, the edge-crowns on the obverse and the reverse surface side cannot be lower simultaneously by varying the growth rate.
The height of the rear crowns will be lower if the protecting film for preventing autodoping is not provided on the reverse surface side. However, when an epitaxial layer is grown by vapor-phase reaction on a heavily doped substrate without the protecting film, it entails autodoping which has an adverse effect on an impurity concentration profile in the transition zone of the substrate and on the impurity concentration distribution in the peripheral part of the epitaxial layer.